AN EXPERIMENTAL-STUDY OF THE STABILITY OF LIQUID-FLUIDIZED BEDS

Experiments are performed to determine if a stable state of uniform fluidization exists for the case of fluidization of small particles by liquids. Such stable states are theoretically possible if the fluidized mixture has a sufficiently large effective elasticity, and stabilization is expected to be more pronounced as the particle size is decreased. Experiments were conducted for a wide range of variables by independently varying particle size, particle density and fluid properties. Careful measurements of the presence or absence of instabilities were made through a combination of flow visualizations and quantitative measurements. We observed stable uniform fluidization over a range of fluid velocities between that required for minimum fluidization, umf, and that corresponding to the onset of instability waves, uc. We interpret these experimental results in terms of the recent theory of Batchelor, in which the elasticity is identified with two distinct mechanisms-gradient dispersion and Reynolds stresses due to particle velocity fluctuations. The observed strong dependence of the effective elasticity on the ratio of particle Reynolds number to the fluid/solid density ratio gives support to the conclusion that the main contribution to the elasticity is inertial in origin, and is due to the Reynolds stress due to particle velocity fluctuations. © 1990.